SSH.NET: ScpClient Recursive Download Allows Arbitrary File Write via Server-Controlled SCP Filenames

## Summary `ScpClient.Download(string directoryName, DirectoryInfo directoryInfo)` writes files and directories using names returned by the remote SCP server during recursive downloads, with no validation that the resulting path stays inside the requested local directory. A malicious, compromised, or man-in-the-middle SCP server can return names containing `../` sequences (or absolute paths), causing the client to create directories and write/overwrite files anywhere the client process has access. This is similar to OpenSSH [CVE-2019-6111](https://github.com/advisories/GHSA-jr78-hfw4-xp7g), but with directory traversal capability. ## Impact A malicious/compromised/MITM SCP server can create or write files outside the intended download directory, anywhere the client process can write. Overwriting files such as ~/.ssh/authorized_keys, shell rc files, cron entries, or application binaries/config can lead to persistence, privilege escalation, or remote code execution on the client host. Requires the victim to perform a directory download from the attacker-controlled server. ## Remediation The fixed release ensures that remotely-supplied file and directory names are valid local names such that the constructed local path is contained within the given local directory, and throws `ScpException` when an invalid name is detected. [600be0de543765995a189b5d7cd4efac5007f3ce](https://github.com/sshnet/SSH.NET/commit/600be0de543765995a189b5d7cd4efac5007f3ce)

Source published

12 Aug 2026 15:19:10 UTC

Source modified

18 Aug 2026 18:15:08 UTC

Observed here

23 Oct 2026 16:01:25 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:L

Publisher rating · HIGH